The use of cellulose acetate as a support in articles of manufacture such as photographic elements is well known. In general, organic solvents which cause cellulose acetate to swell have been used to coat polymer layers on cellulose acetate supports. The swelling promotes adhesion between the polymeric layer and the cellulose acetate support. Aqueous polymer compositions generally have not been used to coat polymeric layers on cellulose acetate supports because such layers have not adhered sufficiently to such supports.
There are several disadvantages to the use of only organic solvents in coating polymer layers on cellulose acetate supports. Elaborate and costly machinery is required to prevent escape of organic solvent vapors into the environment. In addition, the solvents themselves are costly and are generally flammable. Such solvents frequently cause the cellulose acetate film base to curl. Control over curl is possible but not without compromising coating versatility or expenditure of additional energy.
The use of organic solvent-water mixtures has been considered for coating polymer layers on the cellulose acetate supports. However, use of such solvent mixtures necessitates recovery of the organic solvents to prevent the escape into the enviroment. The presence of water in the solvents complicates the recovery process.
It is important that coated layers on cellulose acetate supports to be used in photographic elements be able to withstand normal photographic alkaline processing without undergoing any change in adhesion or other properties. It is also important, from an economic standpoint that film scraps such as perforations and waste film be convertable back to an uncoated condition. Treated scraps can then be redissolved and reused in film support manufacturing. Hence, a useful polymeric layer on cellulose acetate film supports must withstand alkaline photographic processing but be dissolved in the alkaline recovery process.